Fix doc generation with Doxygen 1.9.3

Co-authored-by: Even Rouault <even.rouault@spatialys.com>

WKT1 import: correctly deal with missing rectified_grid_angle parameter

createOperations(): improvement for "NAD83(CSRS) + CGVD28 height" to "NAD83(CSRS) + CGVD2013(CGG2013) height"

Cache result of proj_get_type() to help for performance of proj_factors() (fixes #2965)

[Backport 8.2] createOperationsCompoundToCompound(): fix null pointer dereference when connection to proj.db doesn't exist.

createOperationsCompoundToCompound(): fix null pointer dereference when connection to proj.db doesn't exist.

createOperations(): do not stop at the first operation in the PROJ namespace for vertical transformations

PROJStringFormatter::toString(): avoid invalid iterator increment (fixes #2931)

[Backport 8.2] DOC: Add warning in proj_as_proj_string about potential information loss with CRS